ATLANTIC CITY — Stephan Johnson, a junior middleweight from Brooklyn, was carried from the ring on a stretcher after suffering some brain damage after being knocked out in the 10th round of a fight with Paul Vaden on the undercard of the Michael Grant-Andrew Golota undercard.

Doctors at the Atlantic City Medical Center decided to operate last night to relieve swelling in Johnson’s brain. The boxer was on a respirator and had not regained consciousness.

Johnson, who was leading on two scorecards after nine rounds, went down in a neutral corner after being hit by a long left that seemed to catch him on the way down. The back of Johnson’s head hit the bottom rope as he fell.

Referee Earl Morton waved the fight off and called for the ringside doctors before the count reached three. Oxygen was administered and the 31-year-old Johnson was borne out of the arena on a gurney and taken to the Atlantic City Medical Center.

“It doesn’t look good,” said Dr. Charles Wilson, who accompanied Johnson to the hospital. “It was an accumulation of many blows.”

Dr. Rick Snepar, who attended to Johnson in the ring, said the fighter suffered a seizure on the canvas, “which suggests he took some kind of brain damage. It could be very serious.”

Johnson, a former welterweight contender, had missed all of 1994 after undergoing surgery for a detached retina. He had fought three times this year, including a TKO loss to Fitz Vandepool in Toronto in April.

“The same thing happened in that fight,” said Johnson’s trainer, Kenny Woods. “He was ahead in the fight and then he just died, fell apart.”